Ooh it seems we have to use setAngularFactor instead of setDamping: https://www.babylonjs-playground.com/#3EDS3A#484
compoundBody.physicsImpostor.physicsBody.setAngularFactor(X);
where X can be nothing or anything (string, number, Vector3), which is a bit weird
Seems like Bullet’s setAngularFactor is a bit buggy: Rev 2.73 setAngularFactor() ignored? - Real-Time Physics Simulation Forum
It seems setDamping can set a finite angular resistance, but cannot completely prevent rotation, which setAngularFactor can